Before receiving radiation therapy treatment, a computed axial tomography simulation (CAT scan or CT scan) is typically performed. A CT scan is used to help the radiation oncologist map the target treatment area on a patient's body. Dosimetrists and physicists plan the treatment from the CT images. The CT scan is performed with the patient in a comfortable, yet stable position for the area being treated. With the patient in the desired treatment position, a CT scan is performed. Using the images from the scan, an oncologist determines a treatment isocenter. When the oncologist determines the isocenter, a computer generates the coordinates for a laser projecting system. The lasers project beams onto the patient, indicating the three points of the coordinates. The center at which the three points intersect in the body defines the isocenter.
External marks are then placed on the patient's skin and used to align the patient for treatment. These external marks will indicate where the isocenter or center of treatment is within the patient's body. When the patient is aligned to these marks, prior to treatment, the isocenter will fall directly under the central axis of the radiation beam. Lining a patient up to these marks ensures that they are in the same position for treatment as they were at the time of simulation. The marks are then tattooed. These tattoos will be used during the course of treatment to reproduce how the patient was positioned during the CT scan.
There remains a need for improved devices and methods for marking isocenters on a patient's body.